1. Field of the Invention
This invention relates to a disk recording/reproducing apparatus adapted to implement bit compression processing to successively inputted data caused to be in a digital form to record/reproduce them through a disk.
2. Description of the Prior Art
Optical disks can have a recording capacity greater than that of magnetic disks by two to three binary orders of magnitude, and can make a higher speed access than that in a recording medium in a tape form. Further such optical disks can carry out recording/reproduction of data in a manner avoiding contact with a medium, thus advantageously providing excellent durability, etc. For these reason, optical disks have been frequently used in recent years. Of such optical disks, so called CDs (Compact Disks) are the most popularly known.
Meanwhile, in the case of attempting to provide, by using an optical disk, a portable recording/reproducing equipment, particularly a head phone stereo equipment of about so-called pocket size, or a recording and/or reproducing apparatus similar thereto, in existing CDs as described above, for example, there are standardized formats for a CD of a disk diameter of 12 cm and a CD of a disk diameter of 8 cm (so called a CD single type). However, in the case of the disk having a diameter of 12 cm, the outside dimension of the recording/reproducing apparatus becomes too large, resulting in poor portability. For this reason, it is conceivable to use a disk having a diameter of 8 cm or less. However, in the case of attempting to constitute a portable recording and/or reproducing apparatus or an apparatus of about a pocket size by using an optical disk having a diameter of about 8 cm or less, there are the following problems.
First, for standard CD format (CD-DA format) optical disk, on which stereo digital PCM audio signals having a sampling frequency of 44.1 KHz and subjected to 16 bit quantization are recorded, are supplied from the maker side, and only reproduction or playback is conducted on the user side, the reproduction or playback time (recording time) of the disk having a diameter of 8 cm is a short value of about 20 to 22 minutes even at the maximum, so the disk would be unable to entirely record a symphony of classical music. For the reproduction or playback time, about 74 minutes or more at the maximum, the same order as that of the 12 cm CD presently available, would be preferable. Further, in the CD-DA format, recording cannot be carried out on the user side. In addition, a non-contact optical pick-up device is easily affected by mechanical vibration, etc., so deviation in tracking and/or defocusing (deviation infocusing), etc. are apt to occur by vibration, etc. For this reason, in the case of carrying such equipment, very effective measures for suppressing bad influence on the reproducing operation due to deviation in tracking or defocusing, etc. are required.
Further, in a CD-MO format (format using a recordable magneto-optical disk) as an extended format of the standard CD format (CD-DA format), the recording/reproducing time of a disk having a diameter of 8 cm is disadvantageously a short time of about 20 to 22 minutes the same as that of the CD-DA format. In addition, the deviation in tracking and/or defocusing of an optical pick-up device resulting from mechanical vibration, etc. are apt to occur. For this reason, measures for preventing bad influence on the recording/reproducing operation resulting therefrom are required.
In a CD-I (CD-interactive) format, as a mode for recording/reproducing a bit-compressed digital audio signal, respective levels as shown in the following Table are standardized.
TABLE 1 ______________________________________ SAMP- PLAYBACK LING QUANTIZA- TIME FRE- TION BIT BAND STEREO/ LEVEL QUENCY NO. WIDTH MONAURAL ______________________________________ A 37.8 kHz 8 17 kHz 2/4 B 37.8 kHz 4 17 kHz 4/8 C 18.9 kHz 4 8.5 kHz 8/16 ______________________________________
As indicated in Table 1, when a disk recorded, e.g. in the B level mode is reproduced, a reproduced signal is obtained by bit-compressing a digital signal of the standard CD-DA format so that the signal density of the reproduced signal becomes equal to an approximately quadruple value (a value about four times greater than that of the original signal). Accordingly, for example, when all recording data are stereo audio compressed data, reproduction of a time four times (four channels) greater than the standard time can be carried out. As a result, even with an optical disk having a diameter of about 8 cm or less, recording/reproduction of about 70 minutes can be carried out.
Meanwhile, in the above-mentioned CD-I format, because a disk is rotationally driven at the same linear velocity as that of the standard CD-DA format, successive audio compressed data will be reproduced at a rate of 1/n recording units on the disk. Each such unit is called a block or sector. One block (sector) is comprised of 98 frames, and the period is 1/75 seconds. In this instance, n is the above-mentioned reproduction or playback time or a numeric value corresponding to bit compression ratio of data. For example, in the B level stereo mode, n is equal to 4. Accordingly, in the B level stereo mode, a data train in which ones of respective four sectors are respectively caused to serve as an audio sector as indicated below: EQU S D D D S D D D . . .
(S is an audio sector, and D is any other data sector)
are recorded on a disk. It is to be noted that since, at the time of an actual recording, a predetermined encode processing (error correction coding processing and interleaving processing) similar to that for audio data of an ordinary CD format is implemented to the above-mentioned data train, data of the audio sectors S and data of the data sectors D are arranged in a distributed manner in recording sectors on the disk. Here, video data or computer data, can be recorded in any data sector D mentioned above. In the case where bit-compressed audio signals are recorded in the data sector D, a data train (S1, S2, S3, S4, S1, S2, S3, S4 . . . ) in which audio sectors S1.about.S4 of four channels are cyclically arranged in a successive manner will be subjected to encode processing and recorded on the disk.
In the case of recording/reproducing successive audio signals, the above-mentioned four channel audio signals, are connected in a successive manner from the first channel to the fourth channel, are used. By reproducing data of the first channel corresponding to the audio sector S1 from the disk innermost circumference up to the outermost circumference thereafter to return to the disk innermost circumference for a second time to reproduce in turn data of the second channel corresponding to the audio sector S2 up to the outermost circumference to reproduce data of the third channel corresponding to the next audio sector S3 from the disk innermost circumference to the outermost circumference for a second time to finally reproduce data of the fourth channel corresponding to the remaining audio sector S4 from the disk innermost circumference up to the outer circumference for a second time, continuous reproduction of a quadruple time will be carried out.
However, at several times during a continuous reproduction as described above, track jump operations of a long distance (returning from the outermost circumference to the inner circumference) are required. Since such track jump operations cannot be instantaneously carried out, there is the serious problem that reproduced data for that time is lost, so a reproduced sound is interrupted. Further, in order to attempt to record successive audio signals, it is impossible to record, e.g., a signal of the sector S2 alone by the relation of the interleaving processing at the time of recording. For this reason, interleaving processing of data of adjacent sectors S1 and S3, or interleaving processing of data of the peripheral sectors in addition thereto is required. As a result, it is necessary to rewrite signals in sectors already recorded. Accordingly, recording of such successive compressed audio data is very difficult.